The invention relates to a new and improved blow molded neck construction for a bottle or other container, a cap therefor, a method of forming the neck, and molds for forming the neck. More particularly, the present invention relates to a neck finish for a blow molded plastic bottle characterized by the fact that when used with a cap having a plug, for example, an inner skirt, the surface of the neck against which the plug seals is a seal surface without parting lines or parting line defect. A portion of the neck above the seal surface includes an inward directed thin flexible flange and no portion of the neck has a diameter less than that of the seal surface. Hence, the plug seals against a smooth surface and leakage is prevented.
An exemplar of the prior art is U.S. Pat. No. 4,691,834 (xe2x80x9cthe 834 patentxe2x80x9d) which shows an upward inward directed flexible flange sealing against the corner of the intersection of the outer wall of the plug and the underside of the top of the cap. The neck sealing surface is, inherently, somewhat uneven and ragged since the neck is cut or sheared adjacent this sealing surface. In the present invention, however, the neck is trimmed on the edge above and removed from the seal surface, i.e., the trimmed edge is not the portion of the neck which seals against the cap plug. The references cited against the ""834 Patent are likewise distinguishable.
U.S. Pat. Nos. 4,625,876 and 4,798,301 show curved plug contacting surfaces but these are of substantially the same diameters as the inner edge of the flanges which engage the underside of the top of the cap.
U.S. Pat. No. 4,699,286 shows a neck and cap which, in shape, resemble portions of the present invention. The seal surface, however, is between the inwardly extending upper lip of the bottle neck and the a downwardly depending annular plug portion of the cap. Such a sealing surface is, inherently, somewhat uneven and ragged because the neck, like that of the ""834 patent above, is cut or sheared adjacent this seal surface.
Similarly, the ""287 patent also shows a neck and cap which, in shape, resemble portions of the present invention. One seal surface, however, is between the inwardly extending upper lip of the bottle neck and a downwardly depending annular plug portion of the cap. Such a sealing surface is, as noted above, inherently uneven and ragged because the neck is cut or sheared adjacent this sealing surface.
The bottle of the present invention is blow molded in a split mold by techniques well known in the art. The surfaces of the mold which define the neck structure cause the neck shape hereinafter described. An upper portion of the parison above the neck is trimmed or cut from the neck according to conventional practice (e.g. pull-up trim, spin trim, ram-down, etc.). In one neck structure, the circle at which the upper portion of the parison is severed from the neck is the inner edge of an inward-upward slanted flange. The other end of the flange merges into a curved surface which extends inward a greater distance than the aforesaid edge to merge with an internal sealing surface of lesser diameter than said edge. The neck structure above the neck sealing surface may have rapidly changing diameters which form a flexible membrane due to parison stretching in the blow molding process. In one form of the invention, below the sealing surface the exterior of the neck structure slants downward-outward to a horizontal shoulder and then extends downwardly and then outwardly to a second or lower shoulder. Other cap engaging means may be used.
Many of the illustrated modifications of the present invention include neck finishes and caps of the xe2x80x9csnap-onxe2x80x9d variety. In accordance with the present invention, however, screw caps wherein the neck and cap skirt have complementary threads are also illustrated. The fact that the same upper neck structure may be used either with a snap-on or a screw-on cap thus becomes apparent.
A cap with which the neck is used has a top having a depending central plug or inner skirt. The outer surface of the plug or inner skirt seals tightly against the sealing surface of the neck. The cap can also include an outer skirt having internal sealing beads which engage the upper and lower shoulders of the neck to hold the cap in place. Such an outer skirt is not a necessary feature of the present invention because the primary sealing action takes place between the outer surface of the central plug and the sealing surface of the neck. Such a skirt, however, provides an additional tamper-evident feature. Alternatively, the neck may have threads which are engaged by threads on the cap skirt. The lower portion of the outer cap skirt may be removed by the user engaging and pulling a pull tab which causes the lower part of the skirt to disengage at a circumferential score line. Until such lower skirt is removed, the cap and neck are tamper-evident. Other types of neck engaging means may be employed.
Several different ways may be employed to form the neck finishes of the present invention in blow molding operations. One such means employs a conventional blow mold wherein a blow dome is formed above the neck finish with several abrupt bends in the parison between the blow dome and the neck sealing surface. The blow dome is trimmed from the neck in a conventional trimming operation.
In another modification of the invention, the shear steel located above the neck finish insert has a projecting extension which is engaged by an outward projection on the blow pin so that when the blow pin is withdrawn, the two extensions shear the parison above the sealing surface of the neck.
In still another form of the invention, the shear steels have inward projections, and the blow pin has an enlarged upper diameter so that as the molds come together the shear steel projection cuts the parison by shearing against the enlargement of the blow pin.
In still another form of the invention, the shear steel is formed with an outward projection and the blow pin is formed with an outward projection below the level of the shear steel. When the blow pin is raised, the two projections shear the excess parison. In this form of the invention the neck finish is approximately vertical above the sealing surface.
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.